1. Field of the Invention
The invention relates to a method for determining the purity of processed waste glass.
2. Description of the Prior Art
A high degree of freedom from foreign matter must be ensured in the processing of waste glass. Accordingly, the processed waste glass may contain per metric ton a maximum of 20 g of opaque foreign bodies such as ceramics, porcelain or stones and a maximum of 5 g of non-ferrous metals. These high degrees of purity are necessary as currently already up to 95% waste glass is added to the melt. These high degrees of purity must be guaranteed by waste glass processors and must be proved by samples of the processed waste glass. As these samplings occur in regular intervals during the processing and as a result of the very low permissible impurifications, in particular by ceramics, stones, porcelain and non-ferrous metals, it is necessary to have large quantities of samples. As a result of this the analysis of the processed waste glass is very costly.
A method of the kind mentioned above has become known from AT 400 906 B. In this known method the sample quantity is allowed to flow over a free fall track and opaque foreign matter such as ceramics, stone and porcelain portions (referred to below as CSP parts) as well as non-ferrous parts (referred to below as NF parts)which are recognised by the sensors are blown out. Both the CSP parts as well as the NF parts are collected in a foreign matter collection container and the pure glass parts are collected in a pure glass collection container. By the detection of the weight increase of the foreign matter collection container and the previous response of either a sensor responding to NF parts or a sensor responding to CSP parts the subsequent weight increase of the foreign matter collection container is added to the respective group of foreign matter, as a result of which the masses of CSP and NF parts contained in the sample is detected and can be brought into relationship to the mass of glass parts contained in the sample.
It has been noticed that in some cases the residues of labels sticking to pieces of glass, in particular those made from metal-coated paper, lead to a separation of the part as a NF part or an opaque part and is separated as foreign matter although this part could certainly be regarded as a valuable substance and could be used.